Primary or non-rechargeable batteries are available in a variety of physical sizes, chemistries, and voltages. For example, alkaline and carbon-zinc primary batteries are commonly available in AAA, AA, C, and D size cells which provide a nominal output voltage 1.5 volts direct current (VDC). Secondary or rechargeable batteries are likewise available in a variety of physical sizes, chemistries, and voltages. Examples include lithium ion, nickel metal hydride (NiMH), and nickel cadmium (NiCd) batteries which are available in a range of sizes and voltages. NiMH and NiCd batteries, for example, are commonly available in AAA, AA, C, and D size cells which provide a nominal output voltage of 1.2 VDC. Of course, still other battery sizes, chemistries, and voltages are also available.
Electrical appliances which rely on batteries as a source of electrical energy are ubiquitous. These appliances perform a variety of functions and are used in numerous situations, including for example consumer, commercial, industrial, and medical applications. Consequently, portable electric appliances present a wide variety of electrical loads, such as a light source in the case of a flashlight, sophisticated electronic circuitry and displays in the case of computing and medical devices, electric motors in the case of devices which produce motion, heating and cooling devices, and the like. Moreover, these devices are packaged in any number of sizes and shapes, depending on the characteristics of the particular appliance and its application. Generally, however, it is desirable that these portable devices be readily transportable by a human.
The batteries received by these devices are often connected electrically in series so as to provide the voltage needed to power the load. Where relatively larger currents are required, two or more batteries (or groups of batteries connected in series) are sometimes connected electrically in parallel.
While such configurations have proven to be extremely useful, they can present operational issues. Thus, for example, the mixing of primary and secondary batteries, partially discharged batteries, batteries having differing charge states, or batteries having different chemistries can deleteriously affect the performance of the batteries and the operation of the appliance. It can also be difficult or impossible to hot swap batteries during the operation of the appliance.
Another recurring issue is the availability of batteries to power these appliances. A particularly vexing situation arises when batteries of the size or type required by a particular appliance are not readily at hand. While an appliance which accepts batteries of more than one size or type provides additional flexibility, the mixing of different size batteries can likewise deleteriously affect the performance of the batteries and the operation of the appliance.